Somatic modification of the genetic complement of mammalian subjects, including humans, has been attempted using a variety of techniques. For example, adenoviral vectors containing a desired gene can be used directly to infect tissues and organs in situ. More typically, perhaps, cell cultures or suspensions of cells are modified ex vivo and then returned to the intact subject via the bloodstream. For example, an RNA-DNA oligonucleotide (RDO) designed to correct the albino point mutation in the mouse tyrosinase gene was able to correct this condition in cultured albino melanocytes (Alexeed, D., et al., Nature Biotechnol (1998) 16:1343–1346). This work was extended to in vivo correction of the same defect by delivering the RDO in liposomes or by intradennal injection as reported by the same group (Alexeed, D., et al., Nature Biotechnol (1999) 16:1343–1346. Earlier work had described selective gene therapy of hair follicles using a liposome-entrapped lac Z (Li, L., et al., Nature Med (1995) 1:705–706). Preferred recipients of the liposomal compositions were endogenous hair follicles in the anagen phase (Domashenko, A., et al., J. Invest Dermatol (1999) 112:552).
Thus, it has been possible to modify hair follicle cells individually in culture and to modify intact hair follicles in vivo. It has also been shown that cultured mutant skin keratinocytes from patients with lamellar ichthyosis can be safely modified genetically in vitro and then transplanted into nude mice to obtain a normal epidermis (Choate, K. A., et al., Nature Med (1996) 2:1263–1267.) Similarly, keratinocytes cultured individually in vitro can be modified genetically and then transplanted into nude mice to obtain re-formed tissue (Deng, H., et al., Nature Biotechnol (1997) 15:1388–1391). It has also been shown that hair follicles will form from hair follicle dermal sheath cells taken from the scalp of a different individual (Reynolds, J., et al., Nature (1999) 402:33–34).
In short, it has been shown that individual cells can be modified genetically and then transplanted to an intact organism and that individual cells, when transplanted can, under appropriate conditions, form an organized tissue.
Direct application of genes or DNA in general to human skin has also been shown to be effective, at least in terms of immunization with respect to an encoded antigen. This has been reported by a number of groups including Tang, D-C, et al., Nature (1997) 388:729–730; Yu, W-H, et al., J. Invest Dermatol (1999) 112:370–375; Falo, L. D. Jr., Proc Assoc Am Physicians (1989) 111:211–219; Shi, Z., et al., Vaccine (1999) 17:2136–2141; and Tuting, P., et al., J. Invest Dermatol (1998) 111:183–188. Fan, H., et al., Nature Biotechnol (1999) 17:870–872 further showed that to elicit a response to a hepatitis B surface antigen, the gene encoding this antigen was effective when applied to normal skin containing hair follicles. However, skin lacking hair follicles was not a suitable target for vaccination.